JP2695975B2 - Method for producing ethylene copolymer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an ethylene copolymer. More specifically, the present invention is excellent in a stable state without radical polymerization of ethylene at room temperature with a special vinyl monomer which is a solid at room temperature, minimizing the residual amount of unreacted vinyl monomer and preventing the reaction system from being blocked by the vinyl monomer. The present invention relates to a method for producing an ethylene copolymer having weather resistance.

(Prior Art) Ethylene-based polymers have excellent moldability at low cost and have excellent physical properties such as transparency and strength, so that they are practically used in a wide range of fields.

However, since the weather resistance is not always sufficient, there is a limitation in applications where direct sunlight is received outdoors. As a means of improving weather resistance, a method of adding a benzophenone-based UV absorber, a benzotriazole-based UV absorber, a hindered amine-based light stabilizer, or the like is generally used.However, since these additives gradually bleed out, they are stable. The effect is not enough. This tendency is particularly strong in thin products such as films.

For this reason, it has been proposed to increase the molecular weight of the additive in order to reduce the bleed-out property. For example, JP-A-57-137358
JP-A-51-126240, from the viewpoint of bleed-out, the effect of increasing the molecular weight of the additive can be expected, but when added to a nonpolar polymer such as polyethylene, the dispersibility becomes insufficient. It is easy and does not always have a sufficient effect.

JP-A-54-21489 discloses a homopolymer and a polymerizable vinyl compound having a hindered amine as a side chain as an additive having good solubility or compatibility with a polymer and high extraction resistance. At least one double bond
Copolymers comprising a compound containing two compounds have been proposed, but there is no disclosure at all regarding copolymerization with ethylene.

(Problems to be Solved by the Invention) The inventors of the present invention have conducted various studies in view of such a current situation. In particular, the present inventors have found that two or more vinyl monomers having a hindered amine group in a side chain are continuously bonded. The light stability and compatibility of the copolymer were found to be reduced due to the block structure or the presence of ester groups remaining unreacted without reacting, and ethylene and hindered amine were subjected to high-pressure radical polymerization. Surprisingly, when a vinyl group having a side group is polymerized, an ethylene copolymer having a very small block structure in which two or more vinyl monomers having a hindered amine group in the side chain are continuously bonded is excellent. And obtained a patent application.

The present invention is a further development of the invention of the above-mentioned application, and particularly when a room temperature solid monomer is used as a vinyl monomer, the vinyl monomer has poor compatibility with ethylene, so that stable supply to the reaction system and reaction When the unreacted monomer is recycled later, troubles such as blockage of the pipe in the reaction system by the vinyl monomer, suction of the compressor, and adhesion of the monomer to the discharge valve and the pipe may occur. It's about giving a solution.

(Means for Solving the Problems) The present invention provides a method in which ethylene and a vinyl monomer are radically polymerized under a temperature condition of 150 ° C. or more while maintaining a pressure of 1000 kg / cm ² or more by a first stage compressor and a second stage compressor. In a method for producing a copolymer, the vinyl monomer has the following general formula: (Wherein, R ₁ represents a hydrogen atom or a methyl group, R ₂ represents —O— or —NH—, R ₃ represents a hydrogen atom or —CN, and R ₄ represents a hydrogen atom or —CO—CH ₃ ) Is a room temperature solid vinyl monomer, which is dissolved in a solvent selected from aliphatic alcohols and aliphatic esters,
The dissolution is supplied to the suction side of a subsequent compressor to be polymerized, and a copolymer of ethylene and the vinyl monomer containing 0.005 mol% or more and less than 9 mol% of the vinyl monomer is obtained. A method for producing a united product is provided.

[Specific description of the invention]

1. Copolymerized Monomer The monomer used for producing the ethylene copolymer of the present invention is ethylene and a room temperature solid vinyl compound represented by the following general formula.

(Wherein, R ₁ represents a hydrogen atom or a methyl group, R ₂ represents —O— or —NH—, R ₃ represents a hydrogen atom or —CN, and R ₄ represents a hydrogen atom or —CO—CH ₃ ) .

The monomers of the above formula (I) are known and are known in the art,
For example, it can be synthesized by the methods described in JP-B-47-8539 and JP-A-48-65180.

Representative examples of the monomer of the formula (I) are as follows.

4-acryloyloxy-2,2,6,6-tetramethylpiperidine 4-acryloyloxy-1,2,2,6,6-pentamethylpiperidine 4-acryloyloxy-1-ethyl-2,2,6,6 -Tetramethylpiperidine 4-acryloyloxy-1-propyl-2,2,6,6-tetramethylpiperidine 4-acryloyloxy-1-butyl-2,2,6,6-tetramethylpiperidine 4-methacryloyloxy-2 , 2,6,6-tetramethylpiperidine 4-methacryloyloxy-1,2,2,6,6-pentamethylpiperidine 4-methacryloyloxy-1-ethyl-2,2,6,6-tetramethylpiperidine 4- Methacryloyloxy-1-butyl-2,2,6,6-tetramethylpiperidine 4-crotonoyloxy-2,2,6,6-tetramethylpiperidine 4-crotonoyloxy-1-propyl-2,2,6 , 6-tetramethylpipe Lysine 4-acryloylimino-2,2,6,6-tetramethylpiperidine 4-acryloylimino-4-cyano-2,2,6,6-tetramethylpiperidine 4-acryloyloxy-1-acetyl-2,2,2, 6,6-tetramethylpiperidine 4-methacryloyloxy-2,2,6,6-tetramethylpiperidine 4-methacryloylimino-2,2,6,6-tetramethylpiperidine 4-acryloylimino-4-cyano-2, 2,6,6-tetramethylpiperidine 4-methacryloyloxy-1-acetyl-2,2,6,6-
Tetramethylpiperidine The above-mentioned monomer is an essential component for producing the copolymer of the present invention, but a small proportion of a comonomer component can also be copolymerized. Examples of this type of comonomer include vinyl ester acids such as vinyl acetate and vinyl propionate; acrylic esters such as methyl acrylate and ethyl acrylate; methacrylic esters such as methyl methacrylate; and unsaturated carboxylic acids such as acrylic acid and methacrylic acid. Acids, generally 9 mol%
The following is preferred.

2. Production of Copolymer The production method of the copolymer according to the present invention is carried out using a high pressure method and a low density polyethylene production apparatus.

(1) Catalyst The copolymer of the present invention is produced by radical polymerization. Thus, the catalyst used in the process of the present invention is a free radical generating initiator.

For example, oxygen, ditertiary butyl peroxide,
Dialkyl peroxides and derivatives such as tertiary butyl cumyl peroxide and dicumyl peroxide, diacyl peroxides such as diacetyl peroxide and dioctanoyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxide Peroxydicarbonates such as carbonate, tertiary butyl peroxyisobutyrate,
Peroxyesters such as tert-butyl peroxypivalate and tert-butyl peroxylaurate; ketone peroxides such as methyl ethyl ketone peroxide and cyclohexanone peroxide; 2,2
-Bicesterary butyl peroxyoctane, 1,1-
Peroxy ketals such as bis (tert-butylperoxy) cyclohexane, hydroperoxides such as tert-butyl hydroperoxide and cumene hydroperoxide, and azo compounds such as α, α'-azoisobutyronitrile Useful.

(2) Polymerization device It is preferable to carry out polymerization continuously. As the polymerization apparatus, a continuous stirred tank reactor or a continuous tube reactor generally used in a high-pressure radical polymerization method of ethylene can be used.

The polymerization can be carried out as a single zone process using these single reactors, but many reactors can be used in series, optionally connected with a cooler, or the interior can be multi-zone processes. It is also possible to use a single reactor effectively divided into several zones. In the multi-zone method, the reaction conditions in each zone are made different to control the properties of the polymer obtained in each reactor or each reaction zone. It is common to adjust body composition, catalyst concentration, molecular weight regulator concentration, and the like. When using a plurality of reactors connected in series, in addition to a combination of two or more tank reactors or two or more tube reactors, one or more tank reactors and one or more Can also be used.

The polymer formed in one or more reactors is
This can be separated from unreacted monomers and processed as in normal high pressure polyethylene production. The unreacted monomer mixture is mixed with an additional amount of the same monomer, repressurized and recycled to the reactor. The additional amount of monomer added as described above is of a composition that returns the composition of the mixture to that of the original feed. Generally, this additional amount of monomer is separated from the polymerization vessel by weight. It has a composition that approximately corresponds to the composition of the coalescence.

In order to obtain a copolymer having a uniform composition, a tank reactor is preferable.

The catalyst is usually dissolved in a solvent having a small chain transfer effect, and is directly injected into the reactor by a high-pressure pump. The concentration is desirably about 0.5 to 30% by weight.

Examples of suitable solvents are hexane, heptane, white spirit, hydrocarbon oils, cyclohexane, toluene, xylene, higher branched saturated fatty acid hydrocarbons and mixtures thereof.

In high-pressure radical polymerization, a chain transfer agent is generally used for adjusting the molecular weight of the produced copolymer, except for special cases. As the chain transfer agent, all those used in ordinary high-pressure radical polymerization can be used. For example, ethane, propane,
Alkanes such as butane, hexane and heptane: alkenes such as propylene, butene and hexene: alcohols such as methanol, ethanol and propanol: ketones such as acetone and methyl ethyl ketone: aldehydes such as acetaldehyde and propionaldehyde it can.

Of these, gaseous ones are injected into the suction side of the compressor, and liquid ones are injected by a pump.

(3) Supply of vinyl monomer Since these vinyl monomers are solid at room temperature, they need to be dissolved in a solvent before use in a polymerization reaction.

As a solvent for the vinyl monomer, an aliphatic alcohol and an aliphatic ester are used. Specific examples include aliphatic alcohols such as methanol, ethanol, and propanol and aliphatic esters such as formic acid, acetic acid, and propionic acid, such as methyl, ethyl, propyl, and butyl esters. You can also. Among them, methanol and ethyl acetate are:
It is preferable because the chain transfer effect is small, the solubility with the vinyl compound is excellent, and a polymer having a relatively high vinyl monomer content and molecular weight is easily obtained.

Various methods are conceivable for supplying a solution in which a vinyl monomer is dissolved in these solvents to the reaction system.

For example, in a method in which a vinyl monomer solution is mixed with ethylene under a low pressure of less than 50 kg / cm ² and supplied, when pressure is increased to a reaction pressure of 1000 kg / cm ² or more, the vinyl monomer and ethylene are phase-separated in a compressor. The vinyl monomer is separated by the drain separator of the compressor, and the monomer composition concentration supplied to the reactor becomes non-uniform.
Vinyl monomer adheres to the discharge valve and its piping,
Blockage trouble is likely to occur. Further, the product after the polymerization reaction and the unreacted gas are generally separated by a high-pressure product separator and a low-pressure product separator, and the unreacted gas is recycled. It was found that ethylene and vinyl monomer phase-separated in the recycle line of the reaction gas, causing a clogging phenomenon of the piping, which was not preferable.

To avoid this, the vinyl monomer solution is mixed with ethylene under 50 kg / cm ² or more high-pressure, it is necessary to supply to the rear reactor was raised to reaction pressure, for example the reactor in an ultra high pressure pump Although it is conceivable to inject the vinyl monomer solution directly into the system, an ultra-high pressure pump is very expensive and not economical.

Therefore, in the present invention, a method of supplying the vinyl monomer solution to the suction side of the latter-stage compressor is adopted as the method of supplying the vinyl monomer. On the suction side of the latter stage compressor, the pressure separated by a high pressure product separator is usually 150 to 500 kg.
Since / unreacted gases cm ² is recycled by supplying from the compressed to the reaction pressure to the vinyl monomer solution into the reactor to a high vinyl monomers of ethylene and poor compatibility is solid at room temperature compatible It is possible to provide the reaction as a fluid in a state, so that the polymerization reaction is also stable,
This makes it possible to produce an ethylene copolymer in which vinyl monomers are copolymerized uniformly and randomly.

(4) Polymerization conditions The pressure used is 1000 kg / cm ² or more, preferably 1500 to
4000 kg / cm ^2, more preferably in the range of 2000~4000kg / cm ^2.

The polymerization temperature is 150 ° C. or higher, preferably 150 to 300 ° C., more preferably 150 to 250 ° C.

The higher the polymerization temperature, the higher the productivity, but the lower the molecular weight of the copolymer, the more difficult it is to obtain a high molecular weight polymer, and the higher the polymer density in the polymerization system, the more likely the polymerization reaction becomes unstable, Basically a low temperature reaction is preferred.

3. Copolymer In view of the weather resistance and the stability of the polymerization reaction, the ethylene copolymer obtained by the method of the present invention has the above formula (I)
It is desirable that the vinyl monomer represented by is contained in an amount of from 0.005 mol% to less than 9 mol%, preferably from 0.5 to 5 mol%.

Since the copolymer is excellent in weather resistance, particularly in fields where a high degree of weather resistance is required, such as agricultural house films,
It is useful for multi films, various pipes for outdoor use, and related parts. In this case, the number average molecular weight of the copolymer is preferably 10,000 or more.

The present ethylene copolymer can also be used by blending it with another polymer material. In this case, when the blend ratio of the copolymer of the present invention is 5% by weight or less, the number average molecular weight of the copolymer may be less than 10,000, but is preferably 10,000 or more.

When the ethylene copolymer of the present invention is used alone, phenol-based, sulfur-based, phosphorus-based stabilizers, amide-based, metallic soap-based lubricants, silica, and inorganic compounds such as talc may be blended. .

Further, an antistatic agent, a dropping agent, a neutralizing agent, a nucleating agent, other light stabilizers, and the like can also be blended.

When the ethylene copolymer of the present invention is used by blending it with another polymer material, it may be used in combination with the above-mentioned additives.

(Examples) Next, the present invention will be specifically described with reference to examples. In the following examples, the high-pressure polyethylene manufacturing apparatus shown in FIG. 1 was used.

Example 1 Ethylene was supplied from the line 1 at a rate of 40 kg / hour to the suction side of the pre-compressor A, and 4-acryloyloxy-2,2,6,6-tetramethipiperidine was used as a vinyl monomer.
A solution dissolved in ethyl acetate at a rate of 00 g / liter was supplied to the suction side of the latter compressor B by a pump I at a rate of 1.26 liter / hour. Ethyl acetate was supplied as a chain transfer agent at a rate of 7.0 liter / hour to the suction side of the first compressor A by a pump J, and tertiary butyl peroxypivalate was dissolved in normal hexane at a rate of 5 g / liter as a catalyst. the solution was fed to the reactor C by pump K at a rate of from 0.5 l / h, and the polymerization pressure 1900 kg / cm ^2, the polymerization temperature 190 ° C.
The polymerization was carried out.

The reaction mixture flowing out of the reactor C is separated into a high pressure product separator D
The reaction product is separated into a low-pressure product separator E, while the unreacted gas is recycled to a suction side of the second compressor B via a high-pressure recycle gas separator G. The reaction product was granulated from the separator E by a granulating extruder F to obtain a pellet-shaped copolymer.

The MFR (JIS K-6760) of the obtained copolymer was 2.3 g / 10 minutes, and the 4-acryloyloxy-2,2,6,
NMR confirmed that the 6-tetramethylpiperidine component was substantially random, with a content of 0.52 mol%. Further, as a result of analysis by the GPC method, the number average molecular weight of the copolymer was 28,300.

Example 2 Using the same apparatus and method as in Example 1, only the following conditions were changed to produce a copolymer.

2.62 liters / hour of a solution of 4-acryloyloxy-2,2,6,6-tetramethylpiperidine in ethyl acetate, 6.5 liters / hour of ethyl acetate used as a chain transfer agent, and the catalyst was diluted to 10 g / liter in hexane. Was continuously supplied at a rate of 0.82 liter / hour to carry out polymerization.

The MFR of the obtained copolymer was 6.1 g / 10 minutes, and the 4-acryloyloxy-2,2,6,6-tetramethylpiperidine component in the copolymer was substantially random, and the content was 1.05.
NMR confirmed the mole%.

Example 3 Using the same apparatus and method as in Example 1, only the following conditions were changed to produce a copolymer.

5.78 l / h of a solution of 4-acryloyloxy-2,2,6,6-tetramethylpiperidine at 550 g / l which is a saturated dilution concentration in ethyl acetate, and 2.4 l / h of ethyl acetate used as a chain transfer agent. As the catalyst, polymerization was carried out by continuously supplying a solution having a dilution ratio to hexane of 50 g / liter at a rate of 0.86 liter / hour.

The MFR of the obtained copolymer was 13.0 g / 10 minutes, and the 4-acryloyloxy-2,2,6,6-tetramethylpiperidine component in the copolymer was substantially random, and the content was 5%. .
NMR confirmed that it was 0 mol%.

Comparative Example-1 Except that the injection point of the vinyl monomer was changed from the suction side of the latter-stage compressor B of Example-1 to the suction side of the former-stage compressor A which is generally supplied during the production of the copolymer. Production of a copolymer was attempted in the same manner as in Example-1.

As a result, the reaction temperature fluctuated around 200 ° C. ± 10 ° C., and the polymerization reaction was very unstable. About 6 hours after the start of the reaction, the discharge pressure of the pre-compressor A fluctuated, and the low pressure recycling The line filter M was blocked, and it became impossible to continue the subsequent reaction.

As a result of analyzing the copolymer obtained up to the termination of the reaction, the MFR of the copolymer fluctuated as 2.3 to 4.1 g / 10 minutes, and 4-acryloyloxy-2,2,6,6 in the copolymer. -The content of tetramethylpiperidine was as low as 0.1 to 0.6 mol%.
In addition, it was confirmed that the vinyl monomer was bleeding out on the surface of the polymer, and as a result of analyzing the solvent extract of the polymer by gas chromatography, it was found that many unreacted vinyl monomers remained in the polymer. all right.

(Effect of the Invention) In the method of the present invention, it is possible to stably produce the target copolymer without using a room temperature solid vinyl monomer to block the equipment and piping of the reactor. In the obtained copolymer, ethylene and a vinyl monomer are copolymerized substantially at random, and the vinyl monomer can be uniformly dispersed and present in a polymer chain mainly composed of ethylene to be weather-protected. Since the residual amount of the vinyl monomer in the reaction is small, there is no bleed-out of the vinyl monomer, and it is excellent in weather resistance.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a facility for producing a copolymer used in the method of the present invention. 1: Ethylene supply line A: First stage compressor B: Second stage compressor C: Reactor D: High pressure product separator E: Low pressure product separator F: Granulation extruder G: High pressure recycle gas separator H: Low pressure recycle gas separator I: Comonomer injection pump J: Chain transfer agent injection pump K: Catalyst injection pump L: High pressure recycle line filter M: Low pressure recycle line filter

Continuation of the front page (56) References JP-A-2-53804 (JP, A) JP-A-57-180616 (JP, A) JP-A-55-54312 (JP, A) JP-A-58-79033 (JP, A) JP-A-58-38708 (JP, A) JP-A-55-157612 (JP, A) JP-A-54-71185 (JP, A) JP-A-46-43302 (JP, A)

Claims (1)

(57) [Claims] 1. A method for producing an ethylene copolymer by radically polymerizing ethylene and a vinyl monomer under a temperature condition of 150 ° C. or more while maintaining a pressure of 1000 kg / cm ² or more by first and second stage compressors. The vinyl monomer has the following general formula: (Wherein, R ₁ represents a hydrogen atom or a methyl group, R ₂ represents —O— or —NH—, R ₃ represents a hydrogen atom or —CN, and R ₄ represents a hydrogen atom or —CO—CH ₃ ) Is a room temperature solid vinyl monomer, which is dissolved in a solvent selected from aliphatic alcohols and aliphatic esters,
The solution is supplied to the suction side of a post-stage compressor to be polymerized, and a copolymer of ethylene and the vinyl monomer containing the vinyl monomer in an amount of 0.005 to less than 9 mol% is obtained. Manufacturing method of coalescence.